The overall objectives of the proposed research are to determine the biochemical mechanisms by which estrogen and progesterone control the development of endometrial receptivity to the implanting blastocyst and the growth and differentiation of decidualization. These events of early pregnancy require the hormonal regulation of the biochemistry of specific populations of endometrial stromal cells. Cell separation methods will by used in the proposed research to enrich populations of endometrial stromal cells so that estrogen and progesterone receptor levels and rates of DNA, RNA, and protein synthesis can be examined in specific fraction of endometrial cells during preimplantation and decidualization. The following specific aims are proposed: (1) To determine estrogen and progesterone receptor levels in specific populations of deciduoma cells during decidualization. (2) To determine the significance of DNA synthesis during the preimplantation period to the later growth and differentiation of deciduoma cells, and (3) To examine biochemical mechanisms by which specific populations of endometrial cells develop sensitivity to stimuli initiating decidualization. Since both blastocyst implantation and endometrial decidualization involve precise hormonal controls of the biochemistry of discrete populations of endometrial cells, a better understanding of these cellular control mechanisms should contribute to our knowledge of significant events of reproductive physiology.